It is often necessary to determine the period of a periodic signal. For example, the period itself may be a desired measurement, such as when analyzing the operation or quality of electronic or electromechanical equipment, e.g. disk drives. Also, many other measurements of periodic signals require the initial specification of the period for their determination.
Digitizing oscilloscopes are often used to sample, store, and display waveforms from such equipment. Digitizing oscilloscopes contain circuitry for converting analog voltages received at the oscilloscope probes to digital samples, and memory for storing some number of such digital samples. Such oscilloscopes further include circuitry which can analyze the stored samples representing the received signal to determine the period of that signal.
Prior circuitry for finding the period of the input signal from the stored samples calculated the autocorrelation of the stored signal. An autocorrelation at a given time is calculated by multiplying samples of the signal of interest by those of the same signal delayed by the given time, then summing those products. The time at which the autocorrelation is maximum is determined to be the period of the input signal. This approach is an iterative procedure, because the period T.sub.n+1 estimated at step n+1 depends on the previous estimated value T.sub.n. In addition, the same is true with respect to the initial user guess, T.sub.o. Convergence of the {Tn} series to the true value T.sub.PER using this procedure cannot be proven in a mathematically tractable manner for the general case. This process also requires many multiplications, and, thus, is time consuming.
A means for determining the period of an input signal represented by stored samples which is relatively robust, simpler than an autocorrelator, and with predictable outcome is desirable.